Polymer gel with nanocomposite crosslinker

ABSTRACT

A nanocomposite including a metal oxide and two-dimensional nanosheets. The metal oxid includes at least one of zirconia and titania, and the two-dimensional nanosheets include at least one of reduced graphene oxide and boron nitride. A weight ratio of the metal oxide to the two-dimensional nanosheets is in a range of 2:1 to 19:1, or in a range or 2:1 to 9:1. Making the nanocomposite includes forming a first aqueous dispersion including zirconia nanoparticles and graphene oxide powder, combining a reducing agent with the first aqueous dispersion, irradiating the first aqueous dispersion with microwave radiation, thereby yielding a second aqueous dispersion including zirconia and graphene, and separating the nanocomposite from the second aqueous dispersion, wherein the nanocomposite comprises zirconia and graphene.

CLAIM OF PRIORITY

This application is a divisional of and claims the benefit of priorityto U.S. patent application Ser. No. 16/159,303, filed on Oct. 12, 2018,which claims priority to U.S. Provisional Patent Application Ser. No.62/571,478, filed on Oct. 12, 2017, the entire contents of which arehereby incorporated by reference.

TECHNICAL FIELD

This disclosure relates to a polymer gel formed with a nanocompositecrosslinker for water shutoff in oil field applications.

BACKGROUND

Excess water production can limit the lifetime of an oil or gas well,and poses technical, economical, and environmental challenges. Waterproduction is also a factor in oil and gas field damage mechanismsincluding as scale deposition, corrosion, sand production, and mineraldissolution. Polymer gels have been used to reduce water production fromoil and gas fields. However, improvements are needed in polymer thermalstability and salt resistance.

SUMMARY

In a first general aspect, a nanocomposite includes a metal oxideincluding at least one of zirconia and titania, and two-dimensionalnanosheets including at least one of reduced graphene oxide and boronnitride. A weight ratio of the metal oxide to the two-dimensionalnanosheets is in a range of 2:1 to 19:1. In another example, a weightratio of the metal oxide to the two-dimensional nanosheets is in a rangeof 2:1 to 9:1.

In a second general aspect, making a nanocomposite includes forming afirst aqueous dispersion including zirconia nanoparticles and grapheneoxide powder, combining a reducing agent with the first aqueousdispersion, irradiating the first aqueous dispersion with microwaveradiation, thereby yielding a second aqueous dispersion comprisingzirconia and graphene, and separating the nanocomposite from the secondaqueous dispersion, wherein the nanocomposite comprises zirconia andgraphene.

In a third general aspect, a polymer precursor solution includes adispersion including polyacrylamide and a nanocomposite crosslinkerincluding a metal oxide and two-dimensional nanosheets, wherein a weightratio of the nanocomposite crosslinker to the polyacrylamide is in arange of 1:10 to 1:20 and a weight ratio of the metal oxide to thetwo-dimensional nanosheets is in a range of 2:1 to 19:1. In one exampleof the third general aspect, a weight ratio of the metal oxide to thetwo-dimensional nanosheets is in a range of 2:1 to 9:1.

In a fourth general aspect, a polymer gel includes polyacrylamidecrosslinked with a nanocomposite including a metal oxide andtwo-dimensional nanosheets, wherein a weight ratio of the nanocompositecrosslinker to the polyacrylamide is in a range of 1:10 to 1:20 and aweight ratio of the metal oxide to the two-dimensional nanosheets is ina range of 2:1 to 19:1. In one example of the fourth general aspect, aweight ratio of the metal oxide to the two-dimensional nanosheets is ina range of 2:1 to 9:1.

Implementations of the first, second, third, and fourth general aspectsmay include one or more of the following features.

In some implementations, the weight ratio of the metal oxide to thetwo-dimensional nanosheets is about 19:1. In other implementations, theweight ratio of the metal oxide to the two-dimensional nanosheets isabout 9:1. The metal oxide may include, consist of, or consistessentially of zirconia. The two-dimensional nanosheets may include,consist of, or consist essentially of reduced graphene oxide. Thenanocomposite may include, consist of, or consist essentially of reducedgraphene oxide and zirconia.

A weight average molecular weight of the polyacrylamide in the third andfourth general aspects is typically between about 500,000 and about550,000 Daltons.

The details of one or more implementations of the subject matterdescribed in this specification are set forth in the accompanyingdrawings and the following description. Other features, aspects, andadvantages of the subject matter will become apparent from thedescription, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a photograph showing a solution containing a polymer and ananocomposite crosslinker and the resulting polymer gel.

FIG. 2 is a scanning electron microscope (SEM) image of a polymer gel.

FIGS. 3A and 3B show thermogravimetric analysis (TGA) plots of polymergels with and without a nanocomposite crosslinker, respectively.

FIG. 4 depics differential scanning calorimetry (DSC) plots of polymergels with and without a nanocomposite crosslinker.

FIG. 5 shows dynamic mechanical analysis (DMA) plots of polymer gelswith and without a nanocomposite crosslinker.

FIG. 6 shows an X-ray diffraction (XRD) pattern of a polymer gel with ananocomposite crosslinker.

FIGS. 7A and 7B show plots of viscosity versus time at 310 degreesFahrenheit (° F.) for polymer gels with and without a nanocompositecrosslinker, respectively.

FIG. 8 shows differential pressure and leak-off rate versus time for apolymer gel with a nanocomposite crosslinker.

FIG. 9 shows optical microscope image of polymer with a nanocompositegel.

DETAILED DESCRIPTION

Polyacrylamide (PAM) polymer gels formed with nanocomposite crosslinkersdescribed herein demonstrate high temperature stability, mechanicalstability, and salinity resistance, and can be widely applied as watershutoff treatments to mature oil fields with excess water production.The nanocomposite crosslinkers include one or more metal oxides and oneor more two-dimensional (2D) nanosheets. The nanocomposite typicallyincludes a weight ratio of metal oxide to 2D nanosheet in a range of 2:1to 19:1. In one example, the weight ratio of matal oxide to 2D nanosheetis in a range of 2:1 to 9:1. Examples of suitable metal oxides includezirconia and titania. Examples of suitable 2D nanosheets includegraphene oxide (GO), a derivative of graphene oxide, as well as boronnitride (BN). As used in this disclosure, the term “derivative” refersto chemically modified graphene oxide, for example, graphene oxide thatis modified with at least one functional group. Suitable examples offunctional groups include carboxy group, amido group, imino group, andan alkyl group. The chemical modification includes covalent andnon-covalent bonding. Some examples of non-covalent bonding includeelectrostatic and hydrophobic interactions, and Van der Waals forces. Inone example, the term “derivative” refers to a chemically reducedgraphene oxide (RGO), such as graphene oxide that is reduced with ahydrazine hydrate.

The nanocomposite crosslinker can be prepared by a facile,cost-effective, eco-friendly, and scalable chemical reduction methodassisted by in situ microwave irradiation (MWI). In some embodiments,the nanocomposite crosslinker is prepared by forming a aqueousdispersion of 2D nanosheets and nanoparticulate metal oxide, combining areducing agent with the dispersion, and irradiating the dispersion withmicrowave radiation. In some examples, the aqueous dispersion includes 1weight percent (wt %) to 5 wt % of the 2D nanosheets and 1 wt % to 5 wt% of the nanoparticulate metal oxide. The microwave radiation istypically in a range of 500 watts (W) to 1000 W, with a reaction timeranging from 1 minute to 5 minutes. In one example, the 2D nanosheetsare RGO, the nanoparticulate metal oxide is zirconia, and the reducingagent is hydrazine hydrate. Irradiating the dispersion with microwaveradiation reduces the graphene oxide to graphene, yielding a suspensionof a nanocomposite including graphene and zirconia. The nanocomposite isseparated from the suspension, for example, by centrifugation, anddried.

A polymer gel precursor solution can be prepared by combining thenanocomposite and polyacrylamide in water to yield an aqueousdispersion. In some examples, the polymer gel precursor includes 0.2 wt% to 1 wt % nanocomposite and 1 wt % to 4 wt % polyacrylamide. Theaqueous dispersion is heated to yield a polymer gel. In one example, thenanocomposite is dispersed in water, and polyacrylamide is added to thedispersion. Heating the dispersion to yield a polymer gel may includeheating at a temperature of about 300° F. (for example, 310° F.) for alength of time sufficient to form a gel (for example, 2 hours to 4hours).

EXAMPLE

115 milliliters (mL) of concentrated sulfuric acid is mixed with 2 gramsnatural graphite (Merck) to yield a mixture of partially oxidizedgraphite. The temperature of the mixture is maintained below 20 degreesCelsius (° C.). 2.5 g sodium nitrate and 20 g potassium permanganatewere added sequentially while maintaining the temperature below 20degrees Celsius (° C.). The resulting mix was then heated at 35-40° C.for 2 hours followed by addition of 230 ml of deionized water withtemperature controlled under 50° C. The reaction was terminated with 20mL of hydrogen peroxide and resulting graphene oxide was washed with 10%HCl to remove metal ions and deionized water until neutral pH isobtained. The graphene oxide residue was then dried at 60° C. to obtaindry graphene oxide for use in gels.

Experiment 1: 20 g of tetra-n-butylammonium bromide (TBAB) was dissolvedin 250 mL ammonia (500 mL, 1.62 moles) at 80° C. To this solution, 700mL aqueous 1 molar (M) ZrOCl₂ was added dropwise. The resulting mixturewas stirred for 3 hours at room temperature to yield a transparentsolution. The transparent solution was aged (sol maintained) for 24hours at 100° C. in a water bath to form a gel. Deposited ZrOCl₂ in theTBAB template was filtered and dried at 80° C. for 2 days in an oven toyield a zirconia support. The zirconia support was calcined at 500° C.at a rate of 1° C. per minute for 3 hours under isothermal conditions.Experiment 2: 5 mg of cetyltrimethyl ammonium bromide (CTAB) wasdissolved in 250 mL ammonia (500 mL, 1.62 moles) at 80° C. To thissolution, 175 mL of aqueous solution of zirconyl salt (ZrOCl₂) (i.e.65.375 mg ZrOCl₂ dissolved in 250 ml of distilled water) was addeddropwise. The resulting mixture was stirred for 3 hours at roomtemperature to yield a transparent solution. The transparent solutionwas aged (sol maintained) for 24 hours at 100° C. in a water bath toform a gel. Deposited ZrOCl₂ in the CBAB template was filtered and driedat 80° C. for 2 days in an oven to yield a zirconia support. Thezirconia support was calcined at 600° C. at a rate of 7° C. per minutefor 2 hours under isothermal conditions.

400 milligrams (mg) of dried graphene oxide was stirred into 20 mL ofdeionized water until a homogeneous yellow dispersion was obtained.Zirconia was combined with the dispersion in a zirconia:graphene oxideweight ratio of 19:1, and 40 microliters (μL) of hydrazine hydrate wasadded. In another experiment a zirconia:graphene oxide weight ratio of9:1 was used. The resulting dispersion was placed inside a microwaveoven. The microwave oven (2.45 gigahertz (GHz)) was operated at fullpower (1000 W) for 30 second cycles (on for 10 seconds, off and stirringfor 20 seconds) for a total reaction time of 1 to 2 minutes. The yellowdispersion gradually changed to a black color, indicating completion ofthe chemical reduction of the graphene oxide to graphene. The resultingdispersion was centrifuged for 15 minutes (5000 rotations per minute(rpm)) to yield a zirconia/RGO nanocomposite. The zirconia/RGOnanocomposite was dried overnight under vacuum.

Zirconia/RGO nanocomposite was dispersed in water to yield a dispersionincluding 0.2 wt % of the nanocomposite. 4 wt % of polyacrylamide(weight average molecular weight (MW) 550,000, from SNF) was combinedwith the dispersion to yield a polymer gel precursor solution, and thepolymer gel precursor solution was heated at 302° C. for 4 hours toyield a polymer gel. In another experiment, polymer gel precursorsolution was heated at 310° C. FIG. 1 is an image showing polymer gelprecursor solution 100 and the resulting polymer gel 102. FIG. 2 is aSEM image of the polymer gel 102 showing a porous honeycomb-likestructure.

FIGS. 3A and 3B show thermograms of weight loss of a conventionalpolyacrylamide gel (no nanocomposite crosslinker) and a polyacrylamidegel formed as described in this example (4 wt % polyacrylamide and 0.2wt % zirconia/RGO nanocomposite), respectively, as a function oftemperature. The conventional gel included 7 wt % polyacrylamide, 4 wt %formaldehyde, and 10 wt % to 15 wt % methanol in water. Thermogram 300in FIG. 3A shows four main decomposition regimes 302, 304, 306, and 308,starting at 30° C., 80° C., 210° C., and 320° C., respectively. Stage302, up to 80° C., is believed to be due to water evaporation. Stages304 and 306 are attributed to the decomposition of the amide and thecarboxylate side groups of the polyacrylamide, respectively. Stage 308is believed to be due to the decomposition of the polymer backbone. Likethermogram 300, thermogram 310 in FIG. 3B shows four main decompositionregimes 312, 314, 316, and 318. However, thermogram 310 shows a shift ofthe three high temperature regimes 314, 316, and 318 to 127° C., 478°C., and 685° C., respectively, believed to be due to the presence of thezirconia/RGO nanocomposite crosslinkers in polymer gel.

FIG. 4 shows the differential scanning calorimetry (DSC) curves of thepolyacrylamide gel (no nanocomposite crosslinker) and polyacrylamide gelwith nanocomposite formed as described in this example (4 wt %polyacrylamide and 0.2 wt % zirconia/RGO nanocomposite), respectively,as a function of temperature. The significance of this experiment is tostudy the thermal stability of the polymer gel using DSC. The firstendothermic peak (around 0° C.) represents the amount of free waterpresent in the polymer gel while the second endothermic peak is thedegradation enthalpy. As can be seen from the curves in FIG. 4, theamount of free water content remained the same for both gels, while thedegradation enthalpy was reduced by 16% for the gel containingnanocomposite crosslinker. This indicates that less energy was requiredto break the bond between the polymer chains, and between the polymerand the nanocomposite. In addition, the degradation temperature (Tdeg)of the polymer gel reduced from 182° C. to 176° C. when nanocompositewas added. This reduction in Tdeg can be as a result of either (1)graphene acting as a lubricant thus encouraging the polymer molecules tomove pass each other easily at lower temperature, (2) the polymerinterphase was softened with less molecular mobility due to the presenceof the nanocomposite or (3) structural alteration in the polymer chainthat is, the polymer chain was shortened.

FIG. 9 shows the optical microscope images obtained for the polymer withnanocomposite. This image shows that the polymer has short chain that iswell branched entangled. This allows the polymer molecules to move pasteach other easily; making the gel less viscous at lower temperature(complementing the reduction in Tdeg).

FIG. 5 depicts the storage modulus of the polymer gel (withoutnanocomposite crosslinker) in comparison to polymer gel formed asdescribed in this example (4 wt. % polyacrylamide and 0.2 wt. %zirconia/RGO nanocomposite) measured by Dynamic mechanical Analysis(DMA). The elasticity of the polymer gel was enhanced when incorporatedwith the nanocomposite (0.2 wt. % zirconia/RGO). This is evident fromthe 80% increase in storage modulus noted in FIG. 5. This can becredited to the interphase and structural adjustment of the polymer gelin presence of the nanocomposite that caused the stiffness of thepolymer gel to increase.

FIG. 6 shows an X-ray diffraction (XRD) pattern of a polymer gel formedas described in this example (4 wt. % polyacrylamide and 0.2 wt. %zirconia/RGO nanocomposite). FIG. 6 shows peaks at 2 theta (2θ) at about13.9°, 16.7°, 18.5°, 25.3° , and 28.2° , representing diffraction fromthe zirconia and RGO in the polymer gel.

FIGS. 7A and 7B show viscosity at 310° F. as a function of time for aconventional polyacrylamide gel (no nanocomposite crosslinker) and thepolyacrylamide gel of this example (4 wt. % polyacrylamide and 0.2 wt %zirconia/RGO nanocomposite) measured in a high-temperature high-pressureviscometer. The conventional gel included 7 wt. % polyacrylamide, 4 wt.% formaldehyde, and 10 wt. % to 15 wt. % methanol in water. For bothpolymer gels, gel formation occurred after 100 minutes had elapsed. Theinset in FIG. 7A shows a short-lived increase in viscosity to 600 cPafter 100 minutes for the polymer gel without the nanocomposite. FIG. 7Bshows an increase in viscosity to 32000 centipoise (cP) after 100minutes that remained stable and without degradation for at least anadditional 120 minutes, for the gel containing the nanocomposite of thisexample.

FIG. 8 shows results of a core flooding test to evaluate the strength ofthe polyacrylamide nanocomposite gel of this example. The test wasperformed at different pressures, and demonstrated that the resultinggel is stable at a pressure of 2000 pounds per square inch (psi) for 7days with negligible water leak off. Once the curing time (48 hours) iscompleted, the formation brine was injected (post-injection) todetermine the plugging efficiency of the chemical treatment. FIG. 8depicts the pressure drop during all stages with respect to time. Asharp increase in injection pressure with a total differential pressureof 850 psi at the initial injectivity test after chemical curing can beseen. The measured differential pressure is equivalent to 2,550 psi perfoot (ft) holding pressure for the treated matrix by this water shut-offmaterial. Afterward the endurance test was started, and the differentialpressure was held at 800 psi for 1 hour, then 1500 psi for some time.This was followed with an extended period of 180 hours at differentialpressure of 2000 pounds per square inch differential (psid) with minimalleak-off through the treated core plug. The averaged measured leak-offrate during this period was 0.0018 cubic centimeters per minute(cm³/min.) The equivalent drawdown pressure that the core was able towithstand was 6000 psi/ft (2000 psid for a 3-inch core plug) 0.0018cm³/min.

Thus, the polyacrylamide nanocomposite gel of this example was stable atultra-high temperatures (for example, 310° F.) and obtained a pressureof 2000 psi. In comparison, a conventional polyacrylamide gel (nonanocomposite crosslinker) obtained a pressure of 5 psi and droppedsuddenly. In addition, the viscosity of the polyacrylamide nanocompositegel exceeded that of a conventional polyacrylamide gel (no nanocompositecrosslinker) by a factor of 50. Thus, the polyacrylamide nanocompositegels demonstrate enhanced mechanical and thermal stability and cansignificantly reduce excess water production in mature water oil fields.

Certain Embodiments

In some embodiments, this the invention may be described in thefollowing paragraphs 1-36.

Paragraph 1. A nanocomposite comprising:

a metal oxide comprising at least one of zirconia and titania; and

two-dimensional nanosheets comprising at least one of graphene oxide, aderivative of graphene oxide, and boron nitride;

wherein a weight ratio of the metal oxide to the two-dimensionalnanosheets is in a range of 2:1 to 19:1.

Paragraph 2. The nanocomposite of paragraph 1, wherein:

two-dimensional nanosheets comprise a derivative of graphene oxidecomprising reduced graphene oxide; and weight ratio of the metal oxideto the two-dimensional nanosheets is in a range of 2:1 to 9:1.

Paragraph 3. The nanocomposite of paragraph 1, wherein the weight ratioof the metal oxide to the two-dimensional nanosheets is about 19:1.

Paragraph 4. The nanocomposite of paragraph 1, wherein the weight ratioof the metal oxide to the two-dimensional nanosheets is about 9:1.

Paragraph 5. The nanocomposite of paragraph 1, wherein the metal oxidecomprises zirconia.

Paragraph 6. The nanocomposite of paragraph 5, wherein the metal oxideconsists of or consists essentially of zirconia.

Paragraph 7. The nanocomposite of paragraph 1, wherein thetwo-dimensional nanosheets comprise reduced graphene oxide.

Paragraph 8. The nanocomposite of paragraph 7, wherein thetwo-dimensional nanosheets consist of or consist essentially of reducedgraphene oxide.

Paragraph 9. The nanocomposite of paragraph 1, wherein the nanocompositecomprises reduced graphene oxide and zirconia.

Paragraph 10. The nanocomposite of paragraph 9, wherein thenanocomposite consists of or consists essentially of reduced grapheneoxide and zirconia.

Paragraph 11. A method of making a nanocomposite, the method comprising:

forming a first aqueous dispersion comprising zirconia nanoparticles andgraphene oxide powder;

combining a reducing agent with the first aqueous dispersion;

irradiating the first aqueous dispersion with microwave radiation,thereby yielding a second aqueous dispersion comprising zirconia andgraphene; and

separating the nanocomposite from the second aqueous dispersion, whereinthe nanocomposite comprises zirconia and graphene.

Paragraph 12. The method of paragraph 11, wherein a weight ratio of thezirconia nanoparticles and graphene oxide is in a range of 2:1 to 19:1.

Paragraph 13. The method of paragraph 11, wherein a weight ratio of thezirconia nanoparticles and graphene oxide is in a range of 2:1 to 9:1.

Paragraph 14. The method of paragraph 12, wherein the weight ratio ofthe zirconia nanoparticles to the graphene oxide is about 19:1.

Paragraph 15. The method of paragraph 12, wherein the weight ratio ofthe zirconia nanoparticles to the graphene oxide is about 9:1.

Paragraph 16. A polymer precursor solution comprising:

a dispersion comprising polyacrylamide and a nanocomposite crosslinkercomprising a metal oxide and two-dimensional nanosheets, wherein aweight ratio of the nanocomposite crosslinker to the polyacrylamide isin a range of 1:10 to 1:20 and a weight ratio of the metal oxide to thetwo-dimensional nanosheets is in a range of 2:1 to 19:1.

Paragraph 17. The polymer precursor solution of paragraph 16, whereinthe weight ratio of the metal oxide and the two-dimensional nanosheetsis in a range of 2:1 to 9:1.

Paragraph 18. The polymer precursor solution of paragraph 16, whereinthe weight ratio of the metal oxide and the two-dimensional nanosheetsis about 19:1.

Paragraph 19. The polymer precursor solution of paragraph 16, whereinthe metal oxide comprises zirconia.

Paragraph 20. The polymer precursor solution of paragraph 19, whereinthe metal oxide consists of or consists essentially of zirconia.

Paragraph 21. The polymer precursor solution of paragraph 16, whereinthe two-dimensional nanosheets comprise reduced graphene oxide.

Paragraph 22. The polymer precursor solution of paragraph 16, whereinthe two-dimensional nanosheets consist of or consist essentially ofreduced graphene oxide.

Paragraph 23. The polymer precursor solution of paragraph 16, whereinthe nanocomposite crosslinker comprises reduced graphene oxide andzirconia.

Paragraph 24. The polymer precursor solution of paragraph 23, whereinthe nanocomposite crosslinker consists of or consists essentially ofreduced graphene oxide and zirconia.

Paragraph 25. The polymer precursor solution of paragraph 16, wherein aweight average molecular weight of the polyacrylamide is between 500,000and 550,000 Daltons.

Paragraph 26. A polymer gel comprising:

polyacrylamide crosslinked with a nanocomposite comprising a metal oxideand two-dimensional nanosheets, wherein a weight ratio of thenanocomposite crosslinker to the polyacrylamide is in a range of 1:10 to1:20 and a weight ratio of the metal oxide to the two-dimensionalnanosheets is in a range of 2:1 to 19:1.

Paragraph 27. The polymer gel of paragraph 26, wherein the weight ratioof the metal oxide to the two-dimensional nanosheets is in a range of2:1 to 9:1.

Paragraph 28. The polymer gel of paragraph 26, wherein the weight ratioof the metal oxide and the two-dimensional nanosheets is about 19:1.

Paragraph 29. The polymer gel of paragraph 26, wherein the weight ratioof the metal oxide and the two-dimensional nanosheets is about 9:1.

Paragraph 30. The polymer gel of paragraph 26, wherein the metal oxidecomprises zirconia.

Paragraph 31. The polymer gel of paragraph 30, wherein the metal oxideconsists of or consists essentially of zirconia.

Paragraph 32. The polymer gel of paragraph 26, wherein thetwo-dimensional nanosheets comprise reduced graphene oxide.

Paragraph 33. The polymer gel of paragraph 32, wherein thetwo-dimensional nanosheets consist of or consist essentially of reducedgraphene oxide.

Paragraph 34. The polymer gel of paragraph 26, wherein the nanocompositecrosslinker comprises reduced graphene oxide and zirconia.

Paragraph 35. The polymer gel of paragraph 34, wherein the nanocompositecrosslinker consists of or consists essentially of reduced grapheneoxide and zirconia.

Paragraph 36. The polymer gel of paragraph 26, wherein a weight averagemolecular weight of the polyacrylamide is between 500,000 and 550,000Daltons.

Thus, particular implementations of the subject matter have beendescribed. Other implementations are within the scope of the claims.

What is claimed is:
 1. A nanocomposite comprising: a metal oxidecomprising at least one of zirconia and titania; and two-dimensionalnanosheets comprising at least one of graphene oxide, a derivative ofgraphene oxide, and boron nitride; wherein a weight ratio of the metaloxide to the two-dimensional nanosheets is in a range of 2:1 to 19:1. 2.The nanocomposite of claim 1, wherein: two-dimensional nanosheetscomprise a derivative of graphene oxide comprising reduced grapheneoxide; and weight ratio of the metal oxide to the two-dimensionalnanosheets is in a range of 2:1 to 9:1.
 3. The nanocomposite of claim 1,wherein the weight ratio of the metal oxide to the two-dimensionalnanosheets is about 19:1.
 4. The nanocomposite of claim 1, wherein themetal oxide comprises zirconia.
 5. The nanocomposite of claim 1, whereinthe two-dimensional nanosheets comprise a derivative of graphene oxidecomprising reduced graphene oxide.
 6. The nanocomposite of claim 1,wherein the nanocomposite comprises reduced graphene oxide and zirconia.